Habitat

Dugesia tigrina is typically present in lakes, ponds, and streams in temperate regions. It shows negative phototaxis and dwells in the benthic zones of freshwater biomes as a result. The microhabitats for this organism include the undersides of rocks, plant material, and other types of debris found on lake and stream beds. The existing literature does not specify a depth range for the organism, but studies indicate the presence of D. tigrina in lakes at maximum depths of 25 to 40 cm. Dugesia tigrina shows a preference for water temperatures between 13 and 25°C. (Folsom and Clifford, 1978; Gee, et al., 1998; Stokely, et al., 1965; Takano, et al., 2007)

Physical Description

Dugesia tigrina is colloquially known as a flatworm, and it has a body that is flattened dorsoventrally. Additionally, the body plan exhibits cephalization, and the body surface is covered with cilia used to facilitate gliding locomotion. Sensory lobes known as auricles make the head region look triangular, and eyespots called ocelli are found on the head. In terms of coloration, the body is typically brown with white and yellow spots. The average length of Dugesia tigrina is 9 to 15 mm, but body dimensions can vary due to the organism's ability to regenerate lost parts. (Pickavance, 1971; Salo and Baguna, 1984; Sluys, et al., 2010; Smales and Blankespoor, 1978)

Development

Individuals of Dugesia tigrina that are produced sexually hatch from a cocoon, and are typically 2.0 to 4.5 mm in length when first hatched. They are transparent, and have visible yellow yolk cells. As they grow, they use up the yolk, and the spots of pigment grow and darken. Individuals are considered mature after reaching a mean length of 9 mm. (Folsom and Clifford, 1978; Vowinckel and Marsden, 1971)

Reproduction

Dugesia tigrina is hermaphroditic, and only some populations reproduce sexually. There is no courtship process, and when one individual encounters another, it glides on top of it. They either both face the same direction or opposite directions, and the top flatworm moves its head back and forth over either the head or dorsal side of the bottom flatworm, stimulating it. After several minutes, both lift their tail ends, maneuvering so that both ventral sides meet, and the penes are mutually inserted. Copulation can last 1 minute to 1.5 hours, and ends when the pair separates and leaves. Individuals can mate many times in their lives. (Vreys, et al., 2002)

Dugesia tigrina reproduces both sexually and asexually. Some populations reproduce solely sexually, while others reproduce only by fission, and still other populations reproduce both ways. High temperatures (at approximately 26°C) permit asexual transverse fission, whereas lower temperatures (approximately 20°C) yield a preference for sexual reproduction. Some populations therefore switch from asexual fission to mating seasonally. Reproduction for Dugesia tigrina reaches its peak during the summer months. An adult delivers a cocoon that attaches to surfaces by means of a short stalk. The cocoons have mean diameter of 1.30 mm and give rise to a mean of about 4 newborns upon hatching. An individual can produce multiple cocoons during its lifetime. (Folsom and Clifford, 1978; Vowinckel and Marsden, 1971; Vreys, et al., 2002)

Dugensia tigrina produces a cocoon for every group of offspring produced, and provides provisioning. Otherwise, there is no parental care. (Vreys, et al., 2002)

Parental Investment

no parental involvement

pre-hatching/birth

provisioning

Lifespan/Longevity

There is no current record of the highest, lowest, and average lifespans of Dugesia tigrina. Current literature comments that populations of Dugesia tigrina do not show any signs of degenerative aging due to their regenerative capabilities. It is reported that the mortality rates of fed individuals are negligible because they are solely due to experimental accidents. It is also presented in the literature that Dugesia tigrina is able to reabsorb its body tissues and shrink in size to prevent death from famine. (Salo and Baguna, 1984; Sinko and Streifer, 1971)

Behavior

Dugesia tigrina is free-swimming and exhibits gliding locomotion with the help of mucus secretions as well as cilia that cover the body surface. Individuals can be found both independently or in groups. Group foraging has been observed to increase rates of daily per capita ingestion, which drives increased rates of asexual fission. (Cash, et al., 1993; Pickavance, 1971; Smales and Blankespoor, 1978)

Communication and Perception

Dugesia tigrina is considered one of the most primitive animal forms known to possess a central nervous system for higher order perception and integration. These flatworms are equipped with two eyespots called ocelli that appear as dark pigment cups on the anterior dorsal surface. Dugesia tigrina also has two earlike lobes as part of its anterior head region that function in tactile and chemical sensation. These structures, called auricles, have receptors and cilia on them to facilitate such sensation and perception. Gliding mobility is facilitated by cilia covering the body surface, and the organism shows negative phototaxis upon exposure to light. (Smales and Blankespoor, 1978; Takano, et al., 2007)

Food Habits

Being an opportunistic predator, Dugesia tigrina primarily forages on small crustaceans, insect larvae (particularly those of chironomids and mosquitoes), small round worms, and the soft structures of some freshwater sponges. Dugesia tigrina uses its mucus secretions not only for gliding locomotion but also for capturing prey items. It has been observed that D. tigrina exhibits a threshold temperature for feeding. Feeding is significantly reduced or completely stops below a critical temperature of 6°C. (Cash, et al., 1993; Pickavance, 1971)

Predation

Common predators of Dugesia tigrina include freshwater fish, amphibians such as newts, and some insect larvae, including Odonata larvae. Mucus secreted from Dugesia tigrina functions to inhibit being captured by these organisms. Group foraging is reported to increase survival rates. (Cash, et al., 1993; Davies and Reynoldson, 1969)

Ecosystem Roles

Dugesia tigrina serves as prey to a variety of animals, including fish, amphibians, and insects. It is also a predator itself of insects, aquatic worms, and crustaceans. As a significant predator of insect larvae, particularly mosquitoes, Dugesia tigrina has been introduced to catch basins in Ontario to successfully limit the population growth of immature mosquitoes. However, mosquito populations were not observed to be effectively controlled after introducing these flatworms to vernal pools in North Dakota. (Cash, et al., 1993; Davies and Reynoldson, 1969; Meyer and Learned, 1981)

Economic Importance for Humans: Positive

Despite its simple physical structure, Dugesia tigrina is equipped with a central nervous system (CNS) for integrative neuronal communication and has regenerative abilities. Consequently, this flatworm has been increasingly used as a model organism for educational and research purposes to better understand both tissue regeneration as a result of wear and tear and brain development as the main neural processing center in animals. Genetic research at the molecular level is currently underway for these organisms to attempt to shed light on human growth, development, and tissue turnover. Additionally, Dugesia tigrina has been introduced to some bodies of water in an attempt to control mosquito populations through larval predation by these flatworms, to varying degrees of success. (Meyer and Learned, 1981; Salo and Baguna, 1984; Takano, et al., 2007)

Conservation Status

Other Comments

Dugesia tigrina is also referred to as Girardia tigrina in the current literature.

It is suggested that feeding populations of this species do not age and are therefore considered immortal due to their regenerative capabilities.

Mitotic activity for Dugesia tigrina in terms of its growth and regenerative patterns are regulated by a temporal pattern. The rate of mitosis is observed to have an initial maximum 4 to 12 hours after injury, fall to a minimum at 1 day, and then rebound to attain a second maximum after 2 to 3 days. Anterior and posterior regenerative patterns show the most rapid rate of mitotic activity residing near the site of a wound and diminishing at body sections away from an injured body section. (Salo and Baguna, 1984; Sinko and Streifer, 1971)

Contributors

Rosario Saccomanno (author), The College of New Jersey, Keith Pecor (editor), The College of New Jersey, Angela Miner (editor), Animal Diversity Web Staff.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

asexual

reproduction that is not sexual; that is, reproduction that does not include recombining the genotypes of two parents

benthic

Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

fertilization

union of egg and spermatozoan

freshwater

mainly lives in water that is not salty.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

holarctic

a distribution that more or less circles the Arctic, so occurring in both the Nearctic and Palearctic biogeographic regions.

Found in northern North America and northern Europe or Asia.

insectivore

An animal that eats mainly insects or spiders.

internal fertilization

fertilization takes place within the female's body

introduced

referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

solitary

lives alone

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

Salo, E., J. Baguna. 1984. Regeneration and pattern formation in planarians. I. The pattern of mitosis in anterior and posterior regeneration in Dugesia tigrina, and a new proposal for blastema formation. Journal of Embryology and Experimental Morphology, 83: 63-80.

Disclaimer:
The Animal Diversity Web is an educational resource written largely by and for college students. ADW doesn't cover all species in the world, nor does it include all the latest scientific information about organisms we describe. Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts. While ADW staff and contributors provide references to books and websites that we believe are reputable, we cannot necessarily endorse the contents of references beyond our control.

This material is based upon work supported by the
National Science Foundation
Grants DRL 0089283, DRL 0628151, DUE 0633095, DRL 0918590, and DUE 1122742. Additional support has come from the Marisla Foundation, UM College of Literature, Science, and the Arts, Museum of Zoology, and Information and Technology Services.